The invention relates generally to applications whereby it is desirous to introduce or reintroduce gas with liquid flowing through pipes, and/or mix two fluids within a pipe. In particular, this method can be used, but is not so limited, to mix and entrain air and other odorous gas emissions into sewage to reduce odorous gas emissions and to reduce hydrogen sulfide corrosion and abrasive wear in waste water conveyance, collection and treatment systems.
Throughout past decades, sewers have been utilized to efficiently transport waste water or sewage from locations where it was generated to waste water treatment plants and other destinations. These sewers consist generally of pipelines locate below ground level and oriented with a slight downward grade in the direction of the sewage flow. Gravity acts upon the sewage to cause it to flow within the pipelines toward its ultimate destination. These pipelines are sometimes interconnected by xe2x80x9cdrop structuresxe2x80x9d that allow the sewage to flow from one line into the drop structure, drop vertically therewithin, and then to flow out of the drop structure into additional pipes or other structures.
One problem that occurs during the transport of sewage is the release of sulfides from the sewage. Sulfides form as a result of bacterial reduction of sulfates within the sewage in an anaerobic environment. As sewage ages, the level of sulfides increases. Drop structures within a sewer system can provide a beneficial aeration of the sewage flow by introducing additional dissolved oxygen into the flow. The dissolved oxygen reacts with the sulfides, resulting in less chemical volatility in the sewage. This aeration is particularly beneficial where the sewage is fresh and contains a relatively small amount of dissolved sulfides, such as hydrogen sulfide (H2S).
Unfortunately, in most practical applications, sewage contains a significant amount of potentially volatile dissolved molecular hydrogen sulfide gas. Turbulence within the sewage flow can cause this dissolved gas to be released into the surrounding air. Significant sources of turbulence in sewage flow, and hence the emission of hydrogen sulfide gas in a sewer, occur in drop structures such as interceptor drop maintenance holes, joint structures, forcemain discharges and wet well drops in sewer pumping stations. Thus, while drop structures can reintroduce dissolved oxygen into the sewage flow, lowering the level of hydrogen sulfide gas, they can also cause the release of hydrogen sulfide gas. The hydrogen sulfide emissions often cause corrosion with the drop structures and adjacent sewer lines, and cause odor problems even the most elegant, pristine neighborhoods.
One known type of drop structure comprises an influent line, a maintenance hole and an effluent line. The influent line runs almost horizontally at a relatively shallow depth below the ground surface in the form of a pipe. The maintenance hole is located below the street level maintenance hole manhole cover. The maintenance hole is generally cylindrical in shape with a vertical longitudinal axis. The effluent line is another almost horizontal pipe that exits slightly above the bottom of the maintenance hole. Turbulent waste water flow is created when the sewage, which has a substantial amount of potential energy, exits from the influent line near the top of the maintenance hole and tumbles down like a waterfall to the side wall and base of the maintenance hole. Then the sewage pools and eventually flows out the effluent line. This turbulent action releases hydrogen sulfide gas into the air. To reduce the problem of gas release, while still allowing beneficial aeration of the sewage, the potential and kinetic energy in the sewage must be dissipated.
One known method is to create a wall hugging spiral flow down the maintenance hole to dissipate the energy by friction. The spiral flow is generated by the insertion of a vortex form connected to the influent line near the top of the maintenance hole. The vortex form is generally helical in shape and is placed directly below the manhole cover near the top of the maintenance hole. The vortex form channels and diverts the flow from its languid state into a spiral flow descending down the cylindrical wall of the maintenance hole. The vortex form can be made of concrete with applied protective coating, or made of a noncorrosive material, metal or plastic, such as PVC, High Density Polyethylene (HDPE) or other like materials. The vortex form may be manufactured at the factory or on-site.
Two problems remain to be solved when applying this known method of using a vortex form in a drop structure for sewage flows. First, the upstream flow velocities within the influent line are usually not large enough to create a stable spiral flow on the vertical wall of a typical maintenance hole. Thus, the flow, rather than continuing to spiral down the cylindrical wall of the maintenance hole, will generally revert to a turbulent descending flow similar to waterfall, losing the effective energy dissipation of the spiral flow and releasing significant amounts of hydrogen sulfide gas into the air. Second, quite often the maintenance hole is used for additional lateral influent connections at elevations lower than the main influent pipe. Consequently, the lateral influent connections disrupt the spiral flow and create a turbulent waterfall of sewage to the bottom of the maintenance hole, again releasing significant amounts of hydrogen sulfide gas into the air. The additional influent pipe may run in any direction, but at a lower depth than the main influent pipe.
It, therefore, is an object of this invention to provide a method for reducing gas emissions of a fluid through the entraining and mixing of gas with the liquid.
It is also an object of this invention to provide a method for mixing gas with one or more fluids in a conduit.
Another object of this invention is to provide a method for use in sewer drop structures that significantly reduces odorous gas emissions from the sewer.
A further object of the invention is to reduce hydrogen sulfide corrosion in waste water conveyance, collection and treatment systems.
A benefit of this invention is the improved way in which the method helps to protect conveyance or collection systems from abrasive wear.
Another benefit is the way the invention in particular improves the quality of wastewater by wastewater aeration.
The foregoing objects and benefits of the present invention are provided by a method for reducing gas emission and for entraining and mixing gas with liquids. The method comprises channeling a fluid flow though one or more pipes, introducing the flow from the pipe(s) into a conduit or chamber through the use of spiral flows of predetermined radii, reducing such radii to increase centrifugal forces acting upon the flow, introducing gas into the reduced radius flow and continuing the reduced radius flow within the conduit until the gas is substantially entrained within the flow. This method can be implemented through the use of a maintenance hole and an influent line for carrying liquid to the maintenance hole, a vortex form which accepts the liquid from the influent line, the vortex form comprising a spiral channel of decreasing radius disposed substantially within the maintenance hole, and a conduit also disposed within the maintenance hole and fluidly connected to the vortex form and extending substantially downwardly from the vortex form to a flow exit near the maintenance hole base. The fluid flowing from the influent line enters the vortex form and is channeled by the vortex form into a spiral flow with a radius smaller than the maintenance hole wall radius. The reduction in the radius of the channel outer wall causes the centrifugal forces acting upon the fluid flow to increase, forcing the flow to continue in intimate contact with the outer wall of the channel. The fluid then flows from the reduced radius of the vortex channel into the conduit and, aided by gravity and the flow""s acquired rotational velocity, continues its spiral descent towards the maintenance hole base, in substantially intimate contact with the conduit wall. The spiral flow then exits the conduit near the maintenance hole base into an energy dissipating pool.
The method creates an accelerated fluid flow sufficient to create substantial intimate contact with the vortex form and conduit wall throughout the fluid flow""s descent in the maintenance hole. This intimate contact creates frictional forces that reduce the kinetic energy of the flow and inhibit turbulent flow. The reduction in turbulent flow in turn reduces the release of gases, including hydrogen sulfide. In addition, the spiral flow in the conduit creates an air core with reduced pressure in the center of the conduit, inhibiting the escape of any hydrogen sulfide gas into the environment and encouraging the reintroduction of any escaped gas back into the spiral flow and the energy dissipating pool.
In another embodiment of the invention, two influent lines may be used to channel the same or separate flows into the same conduit at two different but proximate locations. The influent lines can originate from a single line or from two distinct lines and may contain the same or different fluids. The flows are then introduced into the conduit through reducing-radius vortices in opposing rotational direction.
In certain embodiments of the invention, it may be advantageous to utilize a vortex form channel with a downwardly sloping base sufficient to create an accelerating spiral flow. The method may also utilize a vortex form incorporating an entrance flume designed to accept the fluid flow from the influent line and more gently direct the flow into the vortex channel. This entrance flume may also incorporate a slope to create an accelerating flow into the vortex channel.
The invention also contemplates utilizing in certain applications of the invention various conduit base configurations for allowing the fluid flow to exit the conduit into the energy dissipating pool. These flow exit paths vary based on the desired fluid flow rates, the energy dissipating pool depth, and the existence and configuration of any effluent lines running from the conduit.
While this invention is particular useful in wastewater conveyance systems, it is not so limited, and can be applied to any system where one desires to mix and entrain one or more gases, including air, into one or more fluid flows within a conduit. Additional applications for the present invention include aeration and/or purification of water in wastewater treatment plants, fishery basins, and natural streams, lakes and bays, and heat transfer in power plant cooling basins. This invention may also be applied to mix food and beverage liquids; to mix constituents in pharmaceutical applications, including applications to suspensions and emulsions; and to mix construction materials including insulation materials, fillers, and high-air concentration mortars and concrete. Thus, the particular embodiments discussed below are not exhaustive and are not intended to limit the scope of this invention.